Catheters are elongate tubular devices sized for introduction into body passages and cavities of a patient, such as a patient's vascular system, gastrointestinal system, abdominal cavity, and the like. A catheter may include one or more lumens intended for passing various other devices, agents, and/or fluids into a body lumen or cavity accessed by the catheter. For such applications, the properties of the inner surface of one or more lumens may significantly impact the performance of the catheter. In particular, the lubricity of the inner surface may affect the ability to pass other devices, agents, and/or fluids through the lumen(s) of the catheter.
To enhance lubricity, it has been suggested to include polytetraflouroethylene (“PTFE”), polyethylene (“PE”) or other cores surrounding the lumen of a catheter. The inner core may be intended to provide a lubricious inner surface to facilitate passing guidewires, pacing leads, or other devices through the lumen of the catheter. Constructing such a catheter, however, is complicated because of the difficulty bonding the inner core to the outer portions of the catheter.
For example, PTFE, in its native form is nearly impossible to bond; consequently, it must be held in place by mechanical interaction or must be etched in order to impart bondability. Further, because of the inaccessibility of the inner surface of the lumen of a catheter, mechanical abrasion or modification, cleaning, etching, application of adhesive, or other modifications of the inner surfaces to facilitate bonding are generally difficult to complete. PE, similar to PTFE, is also difficult to bond to other materials. In some cases, a third material must be used that is bondable both to PE and to other plastics. In both cases, the manufacturing process is complicated and the materials generally expensive.
Other methods for imparting lubricity to inner surfaces have been tried, for example, vapor deposition of surface coatings such as Paralene; however, this process is also complicated and does not result in optimal lubricity.
Hydrophilic coatings are well known and widely used in medical devices. These are readily applied to outer surfaces and frequently used on exteriors of catheters, for example, to facilitate tracking through the vasculature. Nevertheless, application of coatings to catheter exteriors is subject to process limitations. Furthermore, application of such coatings to inner surfaces is currently significantly hindered by technical challenges and therefore not practiced generally.
Hydrophilic coatings are generally dispersed within a solvent, for example, an aqueous or alcohol based solvent, which is applied to a surface and spread evenly in order to deposit a substantially uniform layer of dissolved hydrophilic coating on the surface after evaporation of the solvent. Given the appropriate processing equipment, techniques for coating exterior surfaces of catheters are known. Generally, this is accomplished by dipping. However, inner surfaces, especially small lumens of long catheters, are extremely difficult or impossible to coat because of the difficulty of evenly applying a solution to the inner surface.
For example, the size and geometry of an inner surface, e.g., a small round inner diameter of a catheter, may cause the solution to readily bead up rather than disperse evenly over the surface. Even if the solution could be evenly dispersed over the surface, for example, by addition of surfactants, evaporation of a solvent from inside a long small diameter tube may be slow and irregular, with likely condensation along the way. Thus, this method of coating an inner surface may not be feasible.
Furthermore, once the hydrophilic coating has been evenly deposited, it is often desirable to cross-link or otherwise increase the strength of adhesion of the coating, e.g., using heat or ultraviolet (“UV”) light. In the case of UV light, it may be difficult to expose an inner surface of a catheter to UV light in order to cross-link the coating, unless the material being coated were transparent to UV light. Excessive exposure to UV light may also cause material degradation. Application of heat likewise is not always practicable as it may damage other device components.
With respect to coating outer surfaces, current methods make it relatively difficult to coat discrete sections without masking. Furthermore, the equipment and fixtures required for coating are generally expensive and processes may be difficult to control.
Due to these challenges, surface modification of inner surfaces, as for example, by application of hydrophilic, anti-anti-thrombotic, anti-biotic, drug-eluting, or other coatings is not easily accomplished, although it would be useful in a variety of applications. Furthermore, while coating outer surfaces is often performed, various limitations exist in current processes, which may be improved upon.